Beam regulator



BEAM REGULATOR 4 Sheets-Sheet 5 ATTORNEY.

E. O. LAWRENCE ETAL Z95/ T 1 T Hbz L397 Dec. 4, 1956 Filed March 25, 1948 1956 E. o. LAWRENCE EI'AL 2,773,195

BEAM REGULATOR Tiled March 25, 1948 4 Sheets-Sheet 4 INVENTORS ERNEST 0. LAWRENCE QUENTIN A. KERNS ATTORNEY.

United States Patent O BEAM REGULATOR Ernest 0. Lawrence and Quentin A. Kerns, Berkeley, Calif., assignors to the United States of America as represented by the United States Atomic Energy Commission Application March 25, 1948, Serial No. 16,928

8 Claims. (Cl. 250-419) This invention relates tocalutrons and more particularly to an apparatus for automatically regulating the beam in a calutron.

Calutrons are described in general in Atomic Energy for Military Purposes, by H. D. Smyth, and in great detail in the copending application of Ernest 0. Lawrence, Serial No. 557,784 filed October 9, 1944, now Patent No. 2,709,222.

Calutrons have been principally employed in separating the isotopes of uranium for military atomic energy purposes. They are adaptable to the separation of macroscopic amounts of any mixture of isotopes which may be ionized.

In general an ion source projects ions of the polyisotopic material into a magnetic field. Thereafter the ions travel in curved paths through the magnetic field, the ions of greater mass describing paths with flatter curves than the ions of lighter mass. Collectors are disposed at suitable points along each path, preferably at the 180 point in the curved travel in order to discharge and collect the ions of the different paths. In this manner the atoms of dif ferent mass that were originally in a polyisotopic mixture are distributed in different regions and thereby substantially separated from one another.

The degree of separation of the isotopes which is thus achieved will depend largely upon the stability of the forces acting to produce the aforementioned paths and the accuracy with which the beam is directed upon the collector elements. These forces are the result of the magnetic field and the accelerating potential employed. Of these the accelerating potential lends itself most readily to regulating operations.

It is obvious that variations in the magnetic field, the accelerating field or the position and spacing of the collector pockets will result in improper or faulty separation of the isotopes. These factors become increasingly critical as adjacent isotopes of the heavier elements are treated. This will be apparent from a consideration of mass numbers. For examples: Ca and Ca differ in mass by 2.5% while Pb and Pb differ in mass by less than Since the paths described by the isotopes are a function of these mass differences, it is obvious that the separation of the paths will diminish as heavier elements are treated.

As the result of this diminishing degree of separation between the paths the individual constituents of heavier elements are not resolved into discrete beams but rather are distributed in a series of regions which overlap. Con.- sequently, the separation is not complete but rather an enrichment is achieved in the proportions of the isotopes received in the collectors in favor of the particular isotope which falls principally in that collector element.

Generally, the process of separation is carried out for the purpose of obtaining, in macroscopic quantities, one of the less abundant isotopes.

It is therefore an object of this invention to provide a beam regulator for a calutron wherein the accelerating voltage may be automatically adjusted and regulated so as "ice to maintain stable paths to the collector elements thereby to achieve maximum separation of the polyisotopic mixture.

Another object of the invention is to provide a beam regulator wherein the position of the beam may be determined and adjusted with respect to a preferred collector element whereby errors in spacing between collector ele ments are largely overcome.

Another object of the invention is to provide an apparatus for automatically and accurately directing that portion of the ion beam containing a particular isotope toward a collector element and for regulating the accelerating voltage so as to maintain this condition.

It is a further object of this invention to provide a beam monitoring apparatus which functions independently of calutron dimensions and collector spacing.

Still another object of the invention is to provide a beam monitoring apparatus which functions in the pres ence of sparking or electrical discharge.

The various drawings will now be considered:

Figure 1 is a sectional view of a calutron and a block diagram of the control circuits which attain the objects of the invention;

Fig. 2 is a schematic diagram of the recycler;

Fig. 3 is a schematic diagram of the ripple generator; Fig. 4 is a schematic diagram of the phase detector; Fig. 5 is a schematic diagram of the memory circuit; and Fig. 6 is a schematic diagram of the voltage insertion network.

Fig. 1 diagrammatically illustrates a calutron for the production of uranium enriched in U from a polyisotopic mixture consisting principally of U and U in which U is the more abundant by a factor of approximately 140. Thus the current density of the calutron ion beam is maximum in the region of greatest U density, which region is three mass units or slugs removed from the portion of the beam of maximum U- density.

The calutron includes a beam transmitter 11 and a single pocket receiver 12 provided with a current collector 13. The accelerating voltage supply 14 is of the type wherein the output voltage is regulated from the IR drop across a tapped portion of a voltage dividing network. The high voltage output may be altered; for example, if the voltage dividing resistor is reduced by the fraction without changing the value of the regulating portion, the accelerating voltage will be reduced by the same fraction. t

The positive terminal of the high voltage supply 14 is connected to the ion source through the series arranged voltage regulating network 15, the tapped resistor 16, the voltage insertion network 17 of low resistance and a ripple voltage generator 18 also of low internal resistance, which may inject a low voltage ripple into the accelerating voltage. An operation control network or recycler 19 periodically and for short intervals, causes a three slug resistor within the voltage insertion network to be removed from the circuit, causes a voltage ripple from the ripple generator 18 to be injected into the accelerating voltage, and operatively associates the memory circuit 21 with the phase detector 22. During this interval the accelerating voltage is so regulated by the correction voltage network constituting a portion of the high voltage supply 14 3 cuit 21 maintains the correction voltage constant until the following beam maximizing cycle.

Assuming that suitable power supply equipment is available to provide D. C. potentials of minus 1000, minus 350, minus 150, ground, positive 1105, positive 350, and positive 1000 volts, and filament voltages for (the several vacuum tubes, the means of accomplishing this chain of events will be best understood from the following description and discussion of the control circuits.

In Fig. 2, a schematic diagram of the recycler, the double triode 100AB operates as a Resistance-Capacity oscillator of variable frequency. The cathodes are joined and returned through a common cathode resistor 101 to minus :150 v. from the power supply. The plates are returned through resistors 102 and 103 to the positive 105 volt supply. The grid of triode 100A, one of the two triodes comprising the double triode 100A B is returned to the positive 105 v. supply through an adjustable resistor 104 in parallel with a fixed resistor 106, and also through condenser 107, to the minus 150 volt supply.

The grid of triode 100B is connected to the sliding contactor of a potentiometer 108 one end of which is connected to the minus 150 volt supply and the other end of which is in series with a resistor 1 111 to the plate of the triode 100A.

The above-described circuit constitutes a Resistance- Oapacity oscillator the output of which is obtained from the plate of triode 1003, said output being coupled by condenser 112 to the control grid of the pentode '113 comprising part of a flip-flop circuit. The flip-flop circuit consists of two pentodes 113 and 114 having plate load resistors 116 and 117 respectively connecting their plates to positive 350 v. while their screen grids are tfed from the positive r105 volt supply, through a resistor 118 and bypassed to ground by a condenser 119.

The plate of pentode 1114 is coupled to the suppressor grid of pentode 113 through condenser 121, said suppressor "grid being returned to ground through a resistor 123, while the plate of pentode 113 is coupled to the suppressor grid of pentode 114 through :a condenser 122, the latter suppressor being returned to minus 150 volts through a resistor 125. The cathodes of pentodes 1-13 and 114 are grounded, as is the control grid of pentode 114, while the control grid of pentode 113 is coupled by condenser 124 to the plate of triode 126B and returned to ground through resistor 115. Triodes 126A and 126B have cathodes connected to ground, while the control grid of 126B is returned through resistor 127 to ground, and through a resistor 128 to minus 150 volts, and is coupled to the plate of triode 126A through glow tube 129. The

control grid of triode 126A is connected through resistor 131 to terminal P which leads to a corresponding terminal P of the phase detector to be described later. The plates of triodes 126A and 12613 are connected to positive 105 volts through resistors 132 and 133 respectively,

while a condenser 134 is connected trorn the plate of triode =126A to ground. Between positive 105 volts and ground is connected a voltage divider consisting of a resistor 136 in series with .a potentiometer 137 in series with a resistor 138, the sliding contact of potentiometer 137 being connected to the control grid of triode 126A.

The plates of pentodes 1 13 and 114 lead to terminals R and S respectively which are connected to corresponding terminals of the memory circuit also to be described.

Before considering this circuit, however, let us consider the ripple generator that has been mentioned previously. This is shown schematically in Fig. 3 and consists of circuits as follows: The grid of a triode 141B, part of double triode 141AB is connected to one end of a tuned circuit comprising an inductance 142 in parallel with a condenser 143, the other end of the tuned circuit being grounded. The cathode of triode 141B connects to the juncture of a grounded potentiometer 144 and a resistor 146 connected to minus 150 volts. The slider of potentiometer 144 connects to terminal K which is conneoted to a corresponding terminal K on the voltage insertion circuit as will he described shortly. The plate of triode .141 B receives potential from positive 350 volt supply through series connected resistors 147 and 148, a condenser 149 being connected from their juncture to ground.

T riode 141A is connected as a diode having the plate and grid connected together and to ground, While the cathode is connected to the grid of a triode 1-51-A, one half of double triode 15LAB. The plate of triode 141B is also connected to the grid of triode 151A through coupling condenser 152. The plate of triode 151A is connected to +1350 volts through resistor 153, to the top of the tuned circuit 142, v143 through a resistor 1'54, and to the grid of triode 151 B through resistor 156 in parallel with condenser '15 7 The cathode of triode 151A returns to ground through resistor 158 bypassed by condenser 159. The cathode of triode 151 B is grounded, the plate being connected to +350 volts through resistor 1'61 and to the control grid of pentode 162 through resistor 163 in parallel with condenser 164. The control grid of triode 15113 is also directly connected to the control grid of pentode V166 and to minus 150 volts through resistor 167. The cathodes and suppressors of pentodes 162 and 1 66 are grounded, while the screen grids are connected to positive volts and the plates are connected through resistors 168 and '169 respectively, to positive 105 volts. The control grid of pentode 162 is returned through a resistor 171 to minus volts.

Lt will be seen that pentode 166 receives control grid impulses from the grid of triode 151B while pentode 162 receives control grid impulses from the plate of said triode 151B, thus pentode-s v166 and 162 receive signal voltages having a time phase difference of degrees, and consequently, will have outputs difiering by 180 degrees from each other. Said outputs are obtained from the plates of pentodes 1'66 and 16 2 which are connected to terminals M and L and lead to corresponding terminals of the phase detector which will now be described:

Fig. 4 shows, schematically, the phase detector, with input terminal 0 which is connected externally to the collector element of the calutron as shown in the block diagram Fig. 1. Internally point 0' connects to the cathode cf pentode 172 having plate l'oad resistor 1 73 connected to positive 1000 volts, screen grid connected directly to positive 105 volts, control grid connected via resistor 17 4 to the sliding contact of a potentiometer 176, and suppressor grid returned to the cathode. A condenser 1'80 by-passes input terminal 0 to ground. Potentiometer 176 connects between ground and minus 150 volts. The cathode of pentode 172 in addition to connection to the c-alu-tron collector electrode, returns to the plate of a tetrode 1 77 [through resistor 178 in parallel with condenser 179. Terminal P of the phase detector which connects externally to the corresponding terminal of the recycler Fig. '2, is also connected to the plate of tetrode 177, said 'tetrozde having the screen grid connected to minus 150 volts, the control grid biased to minus 1000 volts through resistor 181 and the cathode returned directly to minus 350 volts. The plateof pentode 172 is coupled through a resistor 182 in parallel with a condenser 1 83 to the control grid of the tetrode 177 while the plate of said tet-rode (point P) is coupled via condenser 185 to the control grid of pentode 184 which grid is connected through resistor 186 to the control grid of pentode .187. The cathodes and suppressor grids of pentodes 1 87, 1'84 and a pentode 1 89 are grounded. The plate of pentode 187 receives voltage from positive 105 volts through resistor 1 88 and is coupled to the control grid of pentode 189 through condenser 1 91 in parallel with a glow tube 192. The control grids of pentodes 187 and 189 are connected together through a resistor 1 93 and the control grid of pentode 1'89 returns through resistor 194 to minus 350 volts. Plate potentials for pentodes 189 and 184 are obtained from the terminals M and L of the phase detector, externally connected to corresponding terminal M and L of the ripple generator circuit of Fig. 3, said potentials consisting of square waves in phase opposition.

The screen grids of pentodes 189 and 184 are joined and connected directly to positive 105 volts as is also the screen grid of pentode 187 while the plates of pentodes 1 84 and 189 are coupled to the control grids of triodes 196A and 196B through condensers 197 and 198 respectively. *Triodes 196A and 196B comprise a pair of cathode followers with a common cathode load resistance. Thus, the plates of triodes 196A and 19GB connect directly to positive 350 volts and the cathodes are joined and connected to minus 150 volts through output resistor 199, while the grids are returned via resistors 201 and 202 to the slider of a potentiometer 203 having one end connected via series resistor 204 to minus 150 volts and the other end connected via series resistor 206 to ground. The single output from the two cathode [followers appears at the cathode end of resistor 199 which is connected to terminal N which leads externally to the input of the memory circuit (terminal N), as shown in the block diagram of Fig. 1 and schematically illustrated in Fig. 5. The memory circuit of Fig. 5 will now he described.

input terminal N of Fig. 5 connects to one stationary contact of a single pole, double throw switch 207, which switch has the transfier arm connected through resistor 208 to the control grid of a pentode 209. The other stationary contact of switch 207 connects to terminal H which connects externally to the corresponding terminal of the voltage insertion network. A condenser 210 is also connected between the control grid of pentode 209 and terminal H. The control grid of pentode 209 is also coupled via :a condenser 212 to the juncture of two condensers 213 and 214. Condenser 213 connects to the control grid of a triode 218A through resistor 216 in parallel with a condenser 217, while condenser 214 Iconnects to the control grid of a triodefi218B through resistor 21 9 in parallel with a condenser 221, said grid being connected through a resistor 220 to terminal H.

Returning momentarily to pentode 209, it will be seen that the plate receives voltage irom positive 1000 volts through a resistor 222, said plate being connected to the plate of triode 218A. Thesuppressor grid of pentode 209 connects to the cathode, which is grounded while the screen grid is connected to positive 105 volts. The control grid of triode 218A is returned through a resistor 223 to positive 105 volts while the cathode is grounded :and the plate is coupled through a resistor 224 in parallel with a condenser 226 to the control grid of triode 227A, half of a dou'hle triode 227AB, said control grid being biased through a resistor 228 in series with resistor 229 to minus 1000 volts. The plate of triode 218B is connected to the cathode of triode 2273 and to the plate and screen grid of a pentode 231. The juncture point between the series connected resistors 2 28 and 229 in the grid return circuit of triode 227A is connected through a glow tube 232 to terminal H previously discuseed, while the cathode of triode 218B and the cathode of triode 227A are joined and connect-ed to the control grid of a triode 233 and through a resistor 234 to minus 350 volts.

The control grid of triode 227B is coupled through a glow tube 236 to terminal H and returned through a resistor 237 to positive 1000 volts, while the plates of triodes 227 A :and 22713 are connected to positive 350 volts. The triode 233, actually a double triode, with similar elements connected in parallel, has positive 350 volts directly connected to its plates, while the cathodes connect to the plate of a tetrode 238 through two glow lamps 239 and 241 in series, said cathode being also returned through a resistor 242 to minus 1000 volts. A resistor 243 is connected across glow lamps 239 :and 241 while the center point between said series connected glow lamps is connected through a resistor 244 to the control grid of pentode 231. .A condenser 246, the so-called memory condenser, connects from the control grid of connected to minus 350 volts, the control grid heing coupled to the juncture of terminals R and I through a resistor 247 in series with a condenser 248, and returned through a resistor 249 to the juncture of resistor 251 and resistor 252 which form a voltage divider across voltages minus 1000 and minus 650. Screen grid potential for tetrode 238 is o'btained from the minus 150 volt supply through .a resistor 253. Terminals R and J are connected together within this, the memory circuit, and ex tern-ally connected to the recycler and the voltage insertion network respectively (Fig. *1)

The cathode and suppressor grid of pentode 231 are connected to terminal H as is the plate of a pentode 254, said pentode 254 having suppressor grid and cathode joined and connected through a cathode resistor 256 to minus 350 volts, while the control .grid is connected through a resistor 257 to ground and through a glow tube 258 to minus 350 volts. The screen grid connects through a resistor 259 to ground and through a resistor 261 to minus 350 volts.

-The insertion voltage circuit which will now be described is shown in Fig. 6. External connections to terminals H and I from the memory circuit and terminal K from the ripple circuit comprise inputs while terminal T connects to the regulator dropping resistor 16 as shown in Fig. 1, :and comprises the output. Internally, as shown in Fig. 6, terminal K, from the ripple generator connects through a resistor 262 in parallel with. a variable condenser 263 to .the control grid of a pentode 264. Terminal H connects to said control grid of pentode 264 through a resistor 266 in parallel with condenser 2'67, and to the control grid of a second pentode 268 through a resistor 269 in parallel with a condenser 271. The cathode of pentode 264 is ground-ed while the screen grid connects directly to positive volts, and the suppressor grid connects to terminal I through a resistor 272 in parallel with a condenser 276 and to minus 350 volts through a resistor 274. The plate of pentode 264 connects through a resistor 276 to positive 11000 volts and through a condenser 278 to the control grid of a triode 279 which control grid is also connected through a resistor 281 in parallel with :a condenser 282 to the plate of pentode 268, and through a resistor 280 to minus 1000 volts.

The plate of said pentode 263 also connects to positive 1000 volts through a resistor 283 while the cathode and suppressor grid of pentode 268 are grounded and the screen grid connected directly to positive 105 volts. In addition to connections previously mentioned the control grid of pentode 268 connects through a resistor 284 in parallel with a variable condenser 286 to the cathode of triode 279 and the plate of a tetrode 287. The triode 279 actually comprises both halves of a double triode with all corresponding elements connected in parallel. The plates are connected directly to positive 350 volts. The plate of tetrode 287 is also connected to a stationary contact of a single pole double throw switch 288 which is arranged for simultaneous operation with the switch 207 shown in Fig. 5. The screen grid of tetrode 287 connects through a resistor 289 to minus 350 volts, and through a resistor 291 to minus 1000 volts while the control grid connects through resistor 2.92 to minus 350 volts and through glow lamp 293 to minus 1000 volts; the cathode returns through a resistor 294 to minus 1000 volts.

The other stationary contact of switch 288 is grounded and the moving contact is by-passed to ground by a condenser 296 and connected to an adjustable resistor 297 in parallel with a condenser 298, The junction of resistor 297 and condenser 298 connects to terminal T and to the control grid of triode 277B. The plate of triode 277B connects to the cathode of triode 277A which also connects through a resistor 299 to the cathode of the same triode 277B. Said cathode of triode 27713 is further connected through a resistor 301 to minus 1000 volts, through a resistor 302 in parallel with a variable condenser 303 to the control grid of pentode 264 and through three series connected glow lamps 304, 306 and 307 to the control grid of triode 277A. The control grid of triode 277A is connected through a resistor 308 to positive 1000 volts, to which the plate of triode 277A is directly connected.

The operation of the circuits will now be considered:

Double triode 1ti0AB of the recycler Fig. 2 and the associated resistance-capacity network comprises an OSClllator of conventional resistance-capacity type having a frequency which may be altered by the adjustable resistance 104 and the potentiometer 108. voltage from the oscillator is coupled by means of the condenser 112 to the control grid of pentode 113 which, in conjunction with pentode 114 comprise a flip-flop circui't. Pentode 113 is normally conducting due to the application of zero bias voltage and Zero suppressor grid voltage, while pentode 114 is normally nonconducting due to the application of minus 150 volts to the suppressor grid through resistor 125. When the control grid of pentode 113 is driven to a sufficiently negative potential by the negative half-cycle of the oscillator voltage, pentode 115 is cut off and the sudden rise in plate voltage which occurs is communicated through condenser 122 to the suppressor grid of pentode 114. This positive pulse on the suppressor grid overcomes the negative voltage normally present and pentode 114 becomes conducting, sharply reducing the voltage at the plate of pentode 114. This is in effect a negative pulse which is communicated to the suppressor grid of the already nonconducting pentode 113, through the condenser 121, thereby further inhibiting conduction in pentode 113. After a period of time determined by the time constant of the charging and discharging circuits, the pentode 113 again begins to conduct causing a negative pulse to appear on the suppressor grid of pentode 114 which causes the latter to become out 011 creating a positive pulse at the plate which communicated by condenser 121 to the suppressor of pentode 113 further promotes conduction. Thus, the circuits revert to a stable condition of equilibrium which remains unchanged until the next pulse from the resistance-capacity oscillator occurs causing a repetition of the cycle. The time constants of the flipflop circuit are relatively short as compared to the trigger repetition rate of the double triode 100AB oscillator circuit. Thus, a positive pulse at terminal R and a negative pulse at S occur, followed shortly by pulses of opposite polarity; after a relatively long period triggering again occurs and the flip-flop cycle is repeated.

Terminals R and S connect to the memory circuit where the pulses are used to initiate a cycle of events as will be described hereinafter.

A second subordinate circuit which produces a necessary component of the acceleration potential during the beam maximizing cycle, will now be discussed.

This is the ripple generator, shown schematically in Fig. 3. Triodes 141B and 151A comprise an oscillator with a frequency which is determined by the inductance 142 and capacity 143 in the grid circuit of triode 141B. Part of the oscillatory energy developed at the plate of triode 151A is coupled back to the grid of triode 141B through the resistor 154, oscillation thus being sustained due to the fact that the grid of triode 141B and the plate of triode 151A are substantially in-phase and positive teed-back results. The output is limited in amplitude to approximately the value of grid bias developed across the cathode resistor 158 and bypass condenser 159, said limiting action occurring because of grid current in triode 151A when the grid is driven positive and because of conduction through the diode connected triode 141A when the grid potential exceeds the bias in the negative direction.

The output A portion of the output voltage from the triode 151A is inverted in the triode 151B and amplified by the pentode 162 while the non-inverted portion is also amplified by pentode 166. Due to the limiting action obtained in the network associated with triode 151A and the degree to which pentodes 162 and 166 are overdriven the resulting outputs from said pentodes 162 and 166 are approximately square waves and differ in phase by 180 degrees due to the inverting action of triode 151B. These square waves, having fundamental frequency components equal to the frequency of the oscillations in the tuned circuit associated with triode 141A, are brought to terminals L and M which lead to the plate of two pentode amplifiers in the phase detector circuit. Said phase detector is shown schematically in Fig. 4.

The collector element of the calutron upon which the desired part of the beam must fall is connected to terminal O which is the input terminal of a two stage current feed-back amplifier comprising tetrode 1'77 and pentode 172. Input terminal 0 is connected to the cathode of pentode 172 which is connected through resistor 178 in parallel with condenser 179 to the plate of tetrode 177. Thus a low impedance path for the flow of the beam current is provided between terminal 0 and ground. Further, the efiective impedance of this path is much lower than it appears since changes in beam current result in very small changes in the potential of the point 0 due to the degenerative action of the circuit which tends to regulate the voltage at said point 0 to a constant value. Pentode 172 operates as a voltage amplifier communicating the small changes in potential at point 0 to the control grid of tetrode 177. The potential thus obtained at the plate of tetrode 177 is a function of the current through the beam, an increase in beam current giving rise to an increase in the potential of point 0 which causes the plate current in pentode 172 to decrease. The plate then becomes more positive and since the plate of pentode 172 is coupled to the control grid of tetrode 177 the control grid of the latter is driven positive causing the potential of the plate to fall. The change in potential at the plate of tetrode 177 comprises the output of the amplifier. It should be noted also that the resulting change in current is in such a direction as to oppose the change in potential of the input due to change in input current. Thus the input has the characteristic of a low impedance since changes in current cause small changes in potential.

A portion of the output thus obtained is inverted by pentode 187 and amplified by pentode 185 while the remaining uninverted portion is amplified by pentode 184. The plate voltages for pentodes 184 and 189 are obtained from the output of the ripple generator and as has been described, these voltages are square Waves, having fundamental frequency components equal to the fundamental frequency of the ripple oscillator and difi'ering in phase from each other by 180 degrees. Since the gains developed by pentode 184 or 189 depend upon the plate voltage supplied, these gains will be alternately large when a maximum portion of the square wave is present and small when a minimum portion or trough is impressed.

Let us assume that the sine wave ripple voltage which was obtained from the cathode of ripple oscillator 141A is injected into the accelerating potential to the ion source of the calutron. The means of obtaining the ripple injection will be described later. The small alternation in accelerating potential due to said ripple causes the speed of the issuing ions from the ion source to rise and fall, which change in speed causes the curvature of the beam path to vary, thus shifting slightly the position of the beam in the region of the collector pocket.

The beam current depends upon the number of ions impinging on the collector electrode and thus will also vary as a function of the ripple voltage. At this point it should be noted that if the portion of the beam having maximum density is centered directly upon the collector electrode any shift in its positionwill tend to result in a decrease in beam current whereas if the beam is not directly centered a shift in the beam in one direction will create an increase in beam current as the beam approaches center and a shift in the opposite direction will cause a decrease in beam current as the beam deviates farther from the center position.

If the case is considered, momentarily, wherein the beam is centered directly upon the collector electrode, the change in current which flows will be very small provided small-amplitude ripple voltage injection is present since the point of operation is the relatively flat top of a typical distribution curve. Thus the current feed-back amplifier comprising vacuum tubes 172 and 177 receives and transmits little signal to the pentodes 189 and 184. However, if the beam is not centered the small ripple component will produce an appreciable variation in the current and a signal to pentodes 184 and 189 will result. It will be noted, further, that if the beam is displaced from the collector element on the side most distant from the ion source which occurs when the accelerator potential is higher than optimum a further increase in acceleration potential will be accompanied by a corresponding fall in beam current, while a fall in acceleration voltage will be accompanied by an increase in beam'current. Thus in this case, it may be said that the ripple voltage and beam current are 180 out of phase.

In the alternate case in which the acceleration potential is low and the beam is displaced from the collector electrode on the side nearest the ion source a small increase in the acceleration potential, as caused by the appropriate half cycle of the ripple voltage, is accompanied by an increase in beam current and conversely, Thus it may be said that the beam current and ripple voltage are in phase when the acceleration voltage is low and 180 out of phase when it is high.

Returning now to the outputs of pentodes 184 and 189, it will be seen that since the plate voltages of 'these amplifiers are square waves in phase opposition and of fundamental frequency equal to that of the ripple voltage, the outputs from said amplifiers will be large in one and small in the other depending on the phase relation between the ripple voltage and the beam current as explained above. These outputs are coupled through condensers 198 and 197 to the two control grids of the triodes 196B and 196A, said triodes compiising a cathode follower circuit having two inputs and a single output, which develops across resistor 199.

The resulting output is a potential which represents the sum of the signals developed by pentodes 184 and 189 and is increased when the beam is displaced from the collector element to the side nearer the ion source and decreased when the beam is displaced to the more distant side of the collector element. Further, this potential has an average value which may be adjusted to a most desired level by potentiometer 203. The output available via terminal N to the memory circuit, is further amplified by pentode 209 within the memory circuit, Fig. 5, and applied through two cathode follower triodes 227A and 233, glow tubes 239 and 241, and resistor 244 to the memory condenser 246 which is. thus charged at a rate determined by resistor 244 and in a direction which is determined by the phase relationship of the collector current and ripple voltage. The charge on the memory condenser 246 is reproduced by the impedance transforming circuit of the cathode follower type in which triode 2273 provides stabilized plate voltage for the cathode follower pentode 231; pentode 254 is a constant current regulator. The potential at the output from this stage follows the charge on the memory condenser and is applied in series with the voltage drop across resistor 266 to the control grid of pentode 264 (see Fig. 6). The three slug resistor 297 connects to the lower end of the voltage dividing resistor 16 which is shown in Fig. 1, and the junction between said voltage dividing resistor and the three slug resistor (point -T) is connected to the control grid of a current regulated cathode follower 277B (Fig. 6) regulated by triode 277A. Thus a voltage exists at the cathode of triode 27715 which is at all times equal to the potential of the lower end of the voltage divider resistor. It is this voltage which is divided by resistors 302 and 266, the part across resistor 266 being applied to the control grid of pentode 264. The pentode 264 is normally in a condition of zero plate current flow by virtue of the negative voltage on the suppressor grid which is overcome during the maximizing cycle by the positive pulse, produced by the recycler, and introduced through the coupling network consisting of resistor 272 and condenser 273. Thus, during the maximizing cycle, the output from pentode 264 is impressed on the grid of regulator triode 279 which is connected from the lower end of resistor 297 to positive 350 volts. The lower end of the resistor 297 returns through a current regulating tetrode 287 to minus 1000 volts. The potential which is thus established at the lower end of the three slug resistor 297 during the maximizing cycle is a direct function of the charge on the memory condenser which is in turn a function of the phase angle between the beam current variation and the ripple voltage. In addition, since the ripple voltage is also applied to the grid of pentode 264 through resistor 262 a ripple component is introduced into the acceleration potential by regulator tube 279.

Upon termination of the current maximizing cycle the recycler produces a negative pulse which restores the pentode 264 to a cut off condition and pentode 268 takes control of regulator tube 279. The pentode 268 is biased from the lower end of the three slug resistor 297 through a divider network, resistors 284 and 269, identical with the divider consisting of resistors 382 and 266 which supplies bias to pentode 264. However, pentode 264 derives bias from the upper end of the three slug resistor 297 by means of the cathode'follower 277B. Thus pentode 268 controls the regulator triode to produce a mean potential at the lower end of three slug resistor 297 which is just equal to the potential which exists at the upper end of said resistor during the maximizing cycle. This in effect comprises an increase in the total accelerating potential by an amount determined by the ratio of the resistance of the three slug resistor 297 to the total high voltage divider resistor which, in the present embodiment involving isotopes of uranium, is in the order of 3 to 23 8, giving rise to the term three slug applied to resistor 297. Thus, during the relatively brief interval of the maximizing cycle the calutron beam is so directed and adjusted that the relatively plentiful ions of uranium having mass numbers 238 are collected in the pocket 12 by collector electrode 13 and the necessary correction voltage is developed by the memory circuit to maximize the beam current thus directed. At the termination of the cycle the change in acceleration voltage which occurs as outlined above is just sufiicient to shift the beam to a new position three mass units farther from the ion source and thus cause the highly desired uranium ions of mass numbers 235 to be collected within the pocket thereby separating them from the U ions which now impinge elsewhere and are disposed of separately. It should be noted thatduring the relatively long interval between maximizing cycles, the memory circuit continues to contribute to the control of the acceleration potential since the memory circuit is coupled to the grid of pentode 268 by resistor 269 and condenser 271.

In order that the charge on the memory condenser be not dissipated during the quiescent period between maximizing cycles, the condenser 246 is disconnected from its charging circuit by the following mechanism:

' During the maximizing cycle triodes 218A and 218B (Fig. 5) are driven to cut off by the negative pulse output from the flip-flop circuit within the recycler, Fig. 2, the negative pulse occurring at the plate of pentode 114.

males 11 However, at the termination of the cycle these tubes become conducting, the input to triode 218B being the output of the cathode follower stage including the pentode 231, which follows the charge on the memory condenser 246. The triode 2183 and associated network constitute a second cathode follower, the output of which is coupled to the grid of triode 233 and causes the cathodes of double triode 233 to reach the same potential as the upper plate of memory condenser 246. Since the potential difference across the neon glow tube 239 is thus reduced to zero said glow tube is extinguished and since tetrode 238 is also driven to cut oif by the negative pulse from the recycler, glow tube 241 is extinguished.

Memory condenser 246 is thus isolated from the charging circuit and since the input impedance of cathode follower circuits are inherently high, said memory condenser retains substantially all its charge until the next maximizing cycle.

If for any reason the current to the collecting electrode 13 should be exceedingly high for a long period, thereby unduly contaminating the concentration of U with U means are provided by the double triode 126AB and associated circuit network for prematurely initiating the succeeding maximizing cycle in order to obtain a correction. For this purpose triode 126A (Fig. 2) is normally biased positively and condenser 134 is nearly completely discharged because of the low plate resistance of conducting triode 126A. When the beam current is high the control grid of triode 126A is driven to cut off by the negative output from current feed-back amplifier stage 177, via terminal P, and condenser 134 commences to charge through the very high resistance 132 toward positive 105 volts. If this situation continues sufficiently long a potential will be reached which causes the neon glow tube 129 to fire producing a sharp positive pulse on the grid of the normally nonconducting triode 126B which in turn produces a sharp negative pulse at the plate which is communicated to the flip-flop circuit comprising pentodes 113 and 114, and which initiates a maximizing cycle.

The entire circuit operation may be summarized briefly as follows:

A signal is periodically developed by the recycler (Figs. 1 and 2) which causes the voltage insertion network to produce a change in average accelerating potential to a value lower than normally present and to superimpose a small alternating voltage or ripple which produces minor excursions of the beam path. During this time the portion of the beam composed predominantly of U ions is directed approximately at the collector element 13. The movements of the beam as the result of the ripple voltage injected, cause variation in the collector current which are or the same phase as the ripple voltage when the average acceleration voltage is below that necessary to attain peak collector current and of opposite phase when said average acceleration voltage is above the value giving peak collector current. These phase relationships are translated by the phase detector into a potential, representing the charge upon a condenser, which is large when the acceleration voltage is low and conversely. This charge is communicated through cathode follower circuits to the voltage insertion network and caused to regulate the total acceleration voltage. This has an immediate effect of bring the beam to the position of maximum collector current and providing a regulating voltage standard to maintain this condition.

However, after a very brief time the recycler produces a second signal which removes the ripple component from the acceleration voltage, returns the total acceleration voltag to a higher potential by a factor of and disassociates the phase detector from the memory condenser which continues to provide a standard voltage for the regulation of tne new acceleration potential. The beam is thus shifted by an amount just sufiicient to cause the portion of the beam composed predominantly of U ions to impinge upon the collector element.

This condition is 12 maintained for a relatively long collecting period before a succeeding maximizing cycle is initiated.

In the event that a spurious result occurs whereby the collector current remains high during the collection period a special maximizing cycle is initiated to prevent a substantial amount of U being collected which is undesirable since undue contamination of the U would result. Contamination during regular maximizing cycles is of negligible importance due to the short duration of the cycle.

At the beginning of operations the switches 207 and 288 which are ganged together, are thrown to the lower positions, which connects the lower end of the three slug resistor 297 directly to ground and which also completely discharges the memory condenser 246. The beam is then maximized on the collector electrode by manual adjustment of the acceleration voltage supply after which the switches are thrown to the other position and the normal cyclic process begins.

It should be noted that this sequence of events in which the position of the beam is determined and adjusted to fall on the collector element after which it is deflected a precise amount with respect to said collector element, in no way depends upon spacing between collectors or any other dimensions of the calutron. Further, the resistor 244, through which the memory condenser 246 is charged causes the rate of change of the charge upon the memory condenser to be small; and irregular and erratic signals caused by arcing and electrical discharge are of little consequence. Also the results of a spurious charge on the memory condenser in the direction causing a high collector current is corrected by the special circuit involving double triode 126AB which initiates a new maximizing cycle.

Errors on the side of high collector current are particularly to be avoided since this condition can occur only when the beam is not positioned correctly but is shifted in the direction of the maximum density region which is composed of U While I have described the salient features of this invention in detail and with respect to the separation of isotopes of uranium specifically, it will be apparent that its use is not confined to this element; furthermore, numerous modifications may be made within the spirit and scope of this invention and I do not therefore desire to limit the invention to the exact details shown except insofar as they may be defined by the spirit and scope of the following claims.

What is claimed is:

1. In a calutron including an ion source and an ion accelerating voltage for forming an arcuate beam of polyisotopic ions and a collecting element disposed in said beam for collecting and discharging a selected portion'of the ions therein, a beam regulator comprising in combination voltage altering means for adjusting said ion accelerating voltage whereby the maximum current portion of said beam of ions is temporarily directed toward said collecting element for a relatively short time-interval suflicient to orient the selected portion of the beam in a desired position with respect to said collector, timing means for periodically altering said ion accelerating voltage a predetermined fraction thereof, whereby the maximum current portion of said beam of ions is deflected a precise distance with respect to said collecting element, and voltage regulating means for maintaining the position of said deflected beam constant for a relatively long time-interval as compared with the interval during which the maximum current portion of said beam is temporarily directed toward said collecting element until said timing means effects a subsequent alteration of said accelerating voltage.

2. In a calutron including an ion source, means including an ion accelerating potential for forming an arcuate beam vof ions and a collector element disposed in said beam for collecting and discharging a selected portion of said ions, a beam regulator comprising in combination,

13 means including a source of alternating voltage for producing minor excursions in the position of said beam of ions, means including a phase sensitive device for comparingthe phase relationship between the current in said ion beam and said alternating voltage and adjusting said ion accelerating potential in consequence thereof so as to temporarily direct the portion of said beam having maximum ionic density toward said collector element for said collecting element whereby a particular orientation of said maximum ionic portion of said beam with respect to said collector is maintained.

3. In a calutron including an ion source and a supply of ion accelerating voltage for forming an arcuate beam of polyisotopic ions, and a collecting element disposed in said beam of ions for collecting and discharging the ions of a selected isotope therein, a beam regulator comprising in combination voltage adjusting means responsive to a characteristic of the discharge current to said collecting element for establishing the ion accelerating voltage required for temporarily directing the maximum current portion of said beam of ions toward said collecting element for a relatively short time-interval sufiicient to orient the maximum current portion of said beam in a desired position with respect to said collector, timing means for periodically altering said ion accelerating voltage a predetermined fraction thereof so as to cause the selected isotope portion of said beam to impinge on said collector,- and voltage regulating means for maintaining said altered accelerating voltage constant during said periodic alteration, whereby a portion of the beam containing the ions of a selected isotope are directed toward said collecting element for a relatively long time-interval as compared with the interval during which the maximum current portion of said beam is temporarily directed toward said collector.

4. In a calutron including a source of polyisotopic ions, ion accelerating electrodes disposed adjacent said ion source, means for applying an accelerating potential between said accelerating electrodes and said ion source whereby a beam of polyisotopic ions is formed, and a collecting element disposed in said beam of ions to collect and discharge the ions of a selected isotope contained therein, a beam regulator comprising in combination, an oscillator and timing means for periodically introducing a component of alternating potential from said oscillator between said accelerating electrodes and said ion source in addition to the normal potential therebetween whereby minor excursions in the position of said beam of ions are produced, means for adjusting said normal accelerating potential in accordance with a relationship between said component of accelerating. voltage and variations in the current flowing to discharge the ions directed toward said collecting element whereby the accelerating potential re quired to temporarily direct the ions of the principal isotope toward said collecting element is established for a relatively short time-interval sufiicient to orient said beam with respect to said collector, means to alter said adjusted accelerating potential a predetermined fraction thereof so as to cause the ions of the selected isotope to impinge on said collector and means for maintaining said altered accelerating potential constant until a succeeding periodic adjustment thereof whereby the selected and predetermined portion of said beam of ions is directed toward said collecting element for a relatively long time-interval as compared with the interval during which the principal 1'4 isotope portion of said beam is temporarily directed to ward said collector.

5. In a calutron including an ion source, ion accelerating electrodes, a source of voltage comprising an ion accelerating voltage connected between said ion source and said accelerating electrodes for forming an arcuate beam of polyisotopic ions, and a collecting element disposed in said beam to collect and discharge the ions of a selected less abundant isotope present therein, a beam regulator comprising in combination, an oscillator, timing means for periodically introducing a ripple voltage from said oscillator into said ion accelerating voltage, means responsive to the phase relationship between said ripple voltage and variations in the current flowing to said collecting element as the result of minor excursions in the position of said beam produced by said ripple voltage for adjusting said ion accelerating voltage to provide the particular accelerating voltage required to temporarily direct the portion of said beam containing a maximum number of ions toward said collecting element for a relatively short time-interval sufiicient to cause the maximum ion portion of said beamto impinge on said collector, further timing means for altering said particular accelerating potential a predetermined fraction thereof so as to cause the ions of the selected isotope to impinge on said collector and be collected therein, and voltage regulating means for maintaining said altered accelerating potential constant for a relatively long interval of time as compared to the interval during which the maximum ion portion of said beam of ions is temporarily directed toward said collecting element.

6. In a calutron including an ion source, ion accelerating electrodes having a source of potential for forming and directing a beam of ions, and a collecting element disposed in said beam to discharge the selected ions received therein, a beam regulator comprising in combination an oscillator for producing an alternating voltage, timing means for periodically introducing said alternating voltage into said source of potential applied to said ion accelerating electrodes, a phase sensitive device responsive to the phase relation between said alternating voltage and variations in the flow of current to said collecting element resulting from minor excursions in the beam position produced by said applied alternating voltage, said phase sensitive device serving to adjust the supply of potential applied to said ion accelerating electrodes whereby a particular accelerating potential is established which temporarily directs the portion of said beam containing the maximum number of ions toward said collecting element for a relatively short time-interval sufficient to position the maximum ion portion of said beam as desired on said collector, means for altering said adjusted accelerating potential a predetermined fraction thereof and means for maintaining said altered accelerating potential constant until a subsequent adjustment thereof whereby the selected portion of said beam of ions is directed toward said collecting element for a relatively long time-interval as compared with the interval during which the maximum ion portion of said beam is temporarily directed toward said collector.

7. In a calutron a beam regulator comprising in combination an ion source, ion accelerating electrodes disposed adjacent said ion source, a regulated power supply for applying an ion accelerating voltage between said ion source and said accelerating electrodes whereby a beam of ions is formed, a current collecting element disposed in said ion beam for collecting and discharging a selected group of the ions in said beam, an oscillator for producing a component of alternating voltage, means including a second oscillator and a trigger circuit for applying said component of alternating voltage upon said accelerating electrodes in short reoccurring intervals whereby minor excursions of said beam are produced, an amplifier connected to said collecting element and a phase sensitive device connected to said amplifier, whereby a regulating 15 voltage is developed in accordance with the phase relationship between said component of alternating accelerating voltage and a resulting variation in current flowing to said collector element, a condenser and means to charge said condenser with said regulating voltage wherebysaid voltage is retained by said condenser, means including a cathode follower circuit for adjusting said ion accelerating voltage in accordance with said regulating voltage upon said charged condenser whereby the maximum ion portion of said beam is temporarily directed toward said collector element for a relatively short timeinterval suflicient to orient said maximum ion portion of said beam with respect to said collector, further means including said second oscillator and said trigger circuit for altering said adjusted accelerating potential a predetermined fraction thereof, whereby a selected portion of said beam of ions is directed toward said collector element for a relatively long time-interval as compared with the interval during which the nonselected portion of said beam is directed toward said collector, and means to isolate said charged condenser from said phase sensitive device whereby said regulating voltage upon said condenser is unchanged and continues to maintain said Y 16 altered accelerating voltage constant until a subsequent adjustment thereof.

8. In a calutron including means for forming an 1211'- cuate beam of ions, a collecting element disposed in said beam for collecting and discharging a selected portion of the ions in said beam, a beam regulator comprising voltage altering means serving to direct the maximum ion portion of the beam temporarily upon said collecting element for a relatively short time-interval suflicient to orient the beam in a desired position with respect to said collector, timing means for periodically deflecting said maximum ion portion of the beam a predetermined distance from said collecting element thereby to cause the selected portion of the beam to impinge upon the collecting element, and voltage regulating means lior maintaining the maximum ion portion of said beam at said deflected position for a relatively long time-interval as compared with the interval during which said maximum ion portion of the beam is temporarily directed upon said collecting element.

No references cited. 

1. IN A CALUTRON INCLUDING AN ION SOURCE AND AN ION ACCELERATING VOLTAGE FOR FORMING AN ARCUATE BEAM OF POLYISOTOPIC IONS AND A COLLECTING ELEMENT DISPOSED IN SAID BEAM FOR COLLECTING AND DISCHARGING A SELECTED PORTION OF THE IONS THEREIN, A BEAM REGULATOR COMPRISING IN COMBINATION VOLTAGE ALTERING MEANS FOR ADJUSTING SAID ION ACCELERATING VOLTAGE WHEREBY THE MAXIMUM CURRENT PORTION OF SAID BEAM OF IONS IS TEMPORARILY DIRECTED TOWARD SAID COLLECTING 